2 * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
11 #include "internal/cryptlib.h"
12 #include <openssl/bn.h>
13 #include <openssl/sha.h>
15 #include <openssl/asn1.h>
17 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
18 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
20 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
21 BIGNUM **rp, const unsigned char *dgst, int dlen);
22 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
23 DSA_SIG *sig, DSA *dsa);
24 static int dsa_init(DSA *dsa);
25 static int dsa_finish(DSA *dsa);
27 static DSA_METHOD openssl_dsa_meth = {
30 dsa_sign_setup_no_digest,
32 NULL, /* dsa_mod_exp, */
33 NULL, /* dsa_bn_mod_exp, */
42 static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
44 void DSA_set_default_method(const DSA_METHOD *meth)
46 default_DSA_method = meth;
49 const DSA_METHOD *DSA_get_default_method(void)
51 return default_DSA_method;
54 const DSA_METHOD *DSA_OpenSSL(void)
56 return &openssl_dsa_meth;
59 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
65 int reason = ERR_R_BN_LIB;
71 if (m == NULL || xr == NULL)
74 if (!dsa->p || !dsa->q || !dsa->g) {
75 reason = DSA_R_MISSING_PARAMETERS;
84 if (ret->r == NULL || ret->s == NULL)
91 if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
94 if (dlen > BN_num_bytes(dsa->q))
96 * if the digest length is greater than the size of q use the
97 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
100 dlen = BN_num_bytes(dsa->q);
101 if (BN_bin2bn(dgst, dlen, m) == NULL)
104 /* Compute s = inv(k) (m + xr) mod q */
105 if (!BN_mod_mul(xr, dsa->priv_key, ret->r, dsa->q, ctx))
106 goto err; /* s = xr */
107 if (!BN_add(ret->s, xr, m))
108 goto err; /* s = m + xr */
109 if (BN_cmp(ret->s, dsa->q) > 0)
110 if (!BN_sub(ret->s, ret->s, dsa->q))
112 if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
116 * Redo if r or s is zero as required by FIPS 186-3: this is very
119 if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
126 DSAerr(DSA_F_DSA_DO_SIGN, reason);
137 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
138 BIGNUM **kinvp, BIGNUM **rp)
140 return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
143 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
144 BIGNUM **kinvp, BIGNUM **rp,
145 const unsigned char *dgst, int dlen)
148 BIGNUM *k, *kinv = NULL, *r = *rp;
153 if (!dsa->p || !dsa->q || !dsa->g) {
154 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
161 if (k == NULL || l == NULL || m == NULL)
164 if (ctx_in == NULL) {
165 if ((ctx = BN_CTX_new()) == NULL)
170 /* Preallocate space */
171 q_bits = BN_num_bits(dsa->q);
172 if (!BN_set_bit(k, q_bits)
173 || !BN_set_bit(l, q_bits)
174 || !BN_set_bit(m, q_bits))
181 * We calculate k from SHA512(private_key + H(message) + random).
182 * This protects the private key from a weak PRNG.
184 if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
187 } else if (!BN_priv_rand_range(k, dsa->q))
189 } while (BN_is_zero(k));
191 BN_set_flags(k, BN_FLG_CONSTTIME);
193 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
194 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
195 dsa->lock, dsa->p, ctx))
199 /* Compute r = (g^k mod p) mod q */
202 * We do not want timing information to leak the length of k, so we
203 * compute G^k using an equivalent scalar of fixed bit-length.
205 * We unconditionally perform both of these additions to prevent a
206 * small timing information leakage. We then choose the sum that is
207 * one bit longer than the modulus.
209 * TODO: revisit the BN_copy aiming for a memory access agnostic
212 if (!BN_add(l, k, dsa->q)
213 || !BN_add(m, l, dsa->q)
214 || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m))
217 if ((dsa)->meth->bn_mod_exp != NULL) {
218 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
222 if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
226 if (!BN_mod(r, r, dsa->q, ctx))
229 /* Compute part of 's = inv(k) (m + xr) mod q' */
230 if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
233 BN_clear_free(*kinvp);
239 DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
248 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
249 DSA_SIG *sig, DSA *dsa)
252 BIGNUM *u1, *u2, *t1;
253 BN_MONT_CTX *mont = NULL;
256 if (!dsa->p || !dsa->q || !dsa->g) {
257 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
261 i = BN_num_bits(dsa->q);
262 /* fips 186-3 allows only different sizes for q */
263 if (i != 160 && i != 224 && i != 256) {
264 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
268 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
269 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
276 if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
279 DSA_SIG_get0(sig, &r, &s);
281 if (BN_is_zero(r) || BN_is_negative(r) ||
282 BN_ucmp(r, dsa->q) >= 0) {
286 if (BN_is_zero(s) || BN_is_negative(s) ||
287 BN_ucmp(s, dsa->q) >= 0) {
293 * Calculate W = inv(S) mod Q save W in u2
295 if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
299 if (dgst_len > (i >> 3))
301 * if the digest length is greater than the size of q use the
302 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
306 if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
309 /* u1 = M * w mod q */
310 if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
313 /* u2 = r * w mod q */
314 if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
317 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
318 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
319 dsa->lock, dsa->p, ctx);
324 if (dsa->meth->dsa_mod_exp != NULL) {
325 if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
329 if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
334 /* let u1 = u1 mod q */
335 if (!BN_mod(u1, t1, dsa->q, ctx))
339 * V is now in u1. If the signature is correct, it will be equal to R.
341 ret = (BN_ucmp(u1, r) == 0);
345 DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
353 static int dsa_init(DSA *dsa)
355 dsa->flags |= DSA_FLAG_CACHE_MONT_P;
359 static int dsa_finish(DSA *dsa)
361 BN_MONT_CTX_free(dsa->method_mont_p);